1. Field of the Invention
The invention relates to a ‘post-construction’ anchor-bolt which is installed into the floor, wall or ceiling after a reinforced concrete frame is matured.
2. Description of the Related Art
Prior post-construction anchor bolts are classified into adhesive anchors and driving anchors (metal-formed extendable anchors), which each consist of various types. In the installation of a post construction adhesive anchor, a capsule filled with adhesive or adhesive itself is embedded into a borehole which has been drilled in advance in a concrete frame, the anchor bolt is inserted, and when the adhesive cures, the concrete and anchor bolt fasten together to complete the installation.
The greatest problem experienced in the installation of conventional post construction anchor bolts is the existence of reinforcement in the concrete. It is not possible to install a post-construction anchor bolt if the anchor bolt borehole encounters reinforcement. Therefore, the inventor proposed a composite anchor bolt which forms a crank, where an anchor bolt projects from the concrete surface and another anchor bolt is embedded inside the concrete. See Japanese Unexamined Patent Publication (kokai) No. 2003-96918.
The disclosure of the specification of the patent publication mentioned above relate to a first anchor bolt, a connecting part, and a second anchor bolt, and their relationship as shown in FIGS. 17 and 18. Specifically, the structure comprises a flat and oblong connecting part 1 with a first anchor bolt 2 installed at one end of the top surface, and a second anchor bolt 3 installed at the opposite end of the underside of connecting part 1. Consequently, the relationship between first and second anchor bolts 2, 3 is that they are mutually on a eccentrically positioned axis. In the installation, connecting part 1 and second anchor bolt 3 are embedded inside concrete frame 4, and first anchor bolt 2 is installed projecting from the surface of concrete frame 4. Thus, even if reinforcement 5 is present in the position of installation for the first anchor bolt, the second anchor bolt can be embedded in a position out of alignment with the position of reinforcement 5 so that the installation can be completed. The first anchor bolt 2 penetrates and projects connecting part 1, this projecting portion is the adhering portion which attaches it to concrete frame 4.
However, for an anchor bolt of a larger diameter, connecting part 1 must also become larger in order to increase the strength of connecting part 1, but it is then not possible to have adhering portion 6 for the first anchor bolt, see FIG. 19. As shown in the figure, the depth of connecting part 1 covers the area of reinforcement covering margin 5.
Said composite anchor bolt works particularly effectively when reinforcement is present in the anchor bolt embedding position. However, if the dimensions are greater, the load on the anchor bolt projecting from the concrete surface will be greater. Therefore, problems can occur, such as bending at the joining point of the connecting part and the anchor bolt (embedded in the concrete), which is caused by an excessive bending moment exerting force on the connecting part Specifically, if tensile force T(KN) acts on the first anchor bolt 2, point C does not shift because of an adequate tensile force between the second anchor bolt and frame, but a bending moment of T×x(KN·cm) does act on point C. If this bending moment increases, joining point C of connecting part 1 and second anchor bolt 3 will bend, therefore damaging the anchor bolt. The concrete adhering margin (the shortest distance between the concrete surface and the reinforcement) is generally 30-60 mm. Therefore, the connecting part can be 30-60 mm thick at the most (in proportion to the diameter of the increasing bolt size). Consequently, the use of the traditional type of anchor bolt cannot be adopted by scale-up only. An anchor bolt having a large diameter can bend easily at point C when there is a bending moment.
The present invention focuses on such conventional problem areas by alleviating the transformation force induced by a bending moment acting on the joining point between the connecting part and the second anchor bolt (even for a larger anchor bolt). The objective of the invention is to provide a post construction composite anchor bolt having good resistance to a bending moment, even if the reinforcement covering margin is shallow, and a method for its installation.